1. Field of the Invention
This invention relates to a shearing machine mounted on a tip of an arm of a working machine, such as a power shovel, for shearing various kinds of steel material.
2. Statement of the Prior Art
When de-constructing or destroying reinforcing bars, buildings of a reinforced concrete construction, scrap steel articles or chemical machinery of steel alloy, a power shovel 1 shown in FIG. 11 is used. The power shovel includes an arm 2 mounted with a steel material shearing machine 3 at the tip end thereof. Such a conventional steel material shearing machine 3 includes a lower jaw 4 and an upper jaw 5. The upper jaw 5 is pivotably connected at the root portion thereof to the rearward portion of the lower jaw 4 by means of a support shaft 6. The upper jaw 5 and the lower jaw 4 are adapted to be opened and closed, in a scissors-like manner, relative to one another by means of a hydraulic cylinder disposed between a frame 7 extending from the lower jaw 4 and the upper jaw 5. The lower jaw 4 and the upper jaw 5 include their respective shearing blades 11, 12 attached to their respective inner surfaces adapted to be slidably engaged with each other. The lower shearing blade 11 attached to the lower jaw 4 and the upper shearing blade 12 attached to the upper jaw 5 are bent at their respective intermediate points 9 outwardly in the open-close direction of the jaws.
The steel material shearing machine 3 shears or cuts a steel material 13 clamped between the lower jaw 4 and the upper jaw 5 when the jaws are moved relative one another in a crossing manner. That is to say, the shearing blades 11, 12 attached to the lower and upper jaws, respectively, serve to shear the steel material 13 in both forward and rearward directions, while preventing slippage of the steel material 13 by reason of the outwardly displaced intermediate points 9.
With the steel material shearing machine 3 having the above construction, the rearward blade portion positioned rearwardly of the intermediate point 9 of each of the lower shearing blade 11 and the upper shearing blade 12 has an angle smaller than that of the forward blade portion. Thus, a cross-angle defined between the steel material and the lower and upper shearing blades 11, 12 becomes smaller as a shearing point of the steel material approaches the respective intermediate points 9, so that shearing ability is reduced at a position adjacent to the intermediate points 9.
It is also noted that the lower jaw 4 and the upper jaw 5 tend to move away from one another by reason of a force component of the shearing force perpendicular to the open-close direction of the lower and upper jaws 4, 5, thus causing so-called "mouth opening" phenomenon, to thereby reduce the shearing ability. The above phenomenon becomes remarkable as approaching the forward end of the blades.
In order to avoid the above "mouth opening" phenomenon, U.S. Pat. No. 4,519,135 discloses a construction in which a side plate is provided with the lower jaw for guiding of the outer side of the upper jaw, whereby the upper jaw is disposed between the lower jaw and the side plate, thus preventing the "mouth opening" phenomenon.
With the above construction, it should be noted, however, that the lower jaw becomes complicated, large in scale, and heavier. It should be noted further that a larger-scale hydraulic cylinder be required, since open-close stroke of the jaws becomes longer.
In order to solve the above problem, the applicant has proposed a steel material shearing machine 3 shown in FIGS. 12 and 13. The shearing machine 3 includes a plurality of lower shearing blades 14, 15 attached to the lower jaw 4. The forward, lower shearing blade (hereinafter referred to as "lower leading blade") 14 and rearward, lower shearing blade (hereinafter referred to as "lower trailing blade") 15 are angled with each other in a V-shaped configuration and staggered relative to one another with respect to the shearing plane as shown in the drawings. The upper jaw 5 also includes a plurality of upper shearing blades 16, 17 attached thereto. The forward, upper shearing blade (hereinafter referred to as "upper leading blade") 16 and the rearward, upper shearing blade (hereinafter referred to as "upper trailing blade") are angled with each other in an inverted V-shaped configuration and staggered relative to one another with respect to the shearing plane. The shearing machine 3 is swivelably mounted on a base frame 20 adapted to be attached to the arm. Thus, the shearing machine 3 is swivelable relative to the base frame 20 by means of an appropriate driving means (not shown).
With the above shearing machine 3, when the upper jaw 5 is closed by means of the hydraulic cylinder 10, the relationship between the interengagement of the upper leading blade 16 and the lower leading blade 14 and the interengagement of the upper trailing blade 17 and the lower trailing blade 15 becomes in opposed manner. Thus, mouth opening phenomenon between the upper leading blade 16 and the lower leading blade 14 can be prevented by reason of the interengagement between the upper trailing blade 17 and the lower trailing blade 15, while mouth opening phenomenon between the upper trailing blade 17 and the lower trailing blade 15 can be prevented by reason of the interengagement between the upper leading blade 16 and the lower leading blade 14. It is also noted that the longitudinally oppositely directed inclination of the blades prevents the steel material 13 from slipping in the longitudinal direction. The above construction permits high shearing ability.